The present invention relates generally to integrated circuits, and more particularly to an integrated circuit having multiple current sources controlled by a common reference.
It is common in integrated circuit design to have a number of current sources controlled by a single reference. The control is commonly accomplished by connecting the bases of the current source transistors to a common reference source. As additional current sources are added, the reference source must provide the additional base current for each added current source.
One prior art method of providing the additional base current is to measure the base current of one of the current sources, then provide a current to the control bus equal to the measured base current times the number of current sources connected to the control bus. This type of compensation has been accomplished in the past using a current mirror circuit where one side of the current mirror has been multiplied using multiple emitters equal to the number of current sources.
While such a compensation circuit should theoretically provide the desired result, it is not as accurate as desired due to base current errors in the mirror and its low output impedance which causes variations in compensation base current with supply voltage.
It would therefore be desirable to provide a circuit that does not vary with supply voltage and having a high output impedance to supply the required base currents for multiple current sources which are coupled to a common reference.